Combustion engines with a common rail injection system are generally known. In this type of combustion engine multiple combustion chambers (and cylinders) are provided. An injector is allocated to each combustion chamber, with each injector connected to a common high pressure rail, (generally called a common rail) for supplying fuel. In common rail systems, due to production tolerances of the injectors (along with other contributing factors), variations with regard to the quantity of fuel injected by individual injectors occur. These differences in the quantity of fuel injected lead to variations in the respective exhaust gas temperatures of the combustion chambers.
One known method to account for this variation is to measure the injection characteristics of each injector after production and to note this on the injector in coded form, for example in the form of a bar code. When the injector is fitted to an engine, this information is then entered into the control unit of the engine by a corresponding reading device. The control unit is then able to control the injectors using their unique, individually measured injection characteristics in order to provide uniform injection among the engine's combustion chambers. This type of method is called Electronic Trim (or e-trim).
The method known as e-trim, however, is rather complex and requires a special reading device when injectors are installed in an engine in order to input the coded information of the individual characteristics of the injector into the engine control unit. For the correct input of this information, a certain degree of training and care are required. Also, with the e-trim method the injection characteristics of the injectors are measured only in the new state. Therefore, the method is not able to take into account the effect of wear and tear which changes the injection characteristics of the injector throughout its service life. This may lead to problems if, for example, a single or several (but not all) injectors are changed on an engine. In this case, the same engine is provided both with new injectors, the injection characteristics of which are known in the new state, and with old injectors, the injection characteristics of which were originally known but which may have changed. However, because the engine control assumes that the old injectors still have the same injection characteristics as in the new state, considerable differences can arise with regard to the injection of fuel into the individual combustion chambers.
In large engines, for example in engines for marine applications, it is known to monitor the exhaust gas temperatures of the individual combustion chambers and to issue a warning if the exhaust gas temperature of a combustion chamber substantially deviates from the exhaust gas temperatures of the other combustion chambers. This type of temperature deviation can be due to different reasons and may indicate a serious malfunction or damage to the combustion engine. One source of exhaust gas temperature deviations is the quantity of fuel which has been supplied to each combustion chamber, and this can depend upon normal tolerances of the fuel injection system. For example, injectors often have flow rate tolerances of +/−5% and more. Some current injectors have a flow rate tolerance of +2.5% and −1.5%.
The purpose of the present disclosure is to improve engine performance and to reduce false alarms from exhaust gas temperature monitoring systems.